1. Field of the Invention
The present invention relates to a nanoparticle array in which groups of nanoscale particles are arranged in an array, a method for producing the nanoparticle array and a magnetic recording medium on which groups of magnetic nanoscale particles are arranged in an array.
This application claims priority of Japanese Patent Application No. 2003-308754, filed on Sep. 1, 2003, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
As the compactness and the high integration of a semiconductor element and the high recording density of a recording medium have progressed, a nanoscale processing technique for producing the element has been required. For instance, in the field of the magnetic recording medium, patterned media in which a nanoscale magnetic material is arranged in the form of a lattice is proposed as a high density magnetic recording media in future (see for instance, a non-Patent Document 1; S. Y. Chou, M. S. Wei, P. R. Krauss, P. B. Fischer, J. Appl. Phys. 1994, 76, 6673.) and the nanoscale processing technique is important as a method for producing the patterned media.
It has been well-known that a photolithography technique usually employed for producing the semiconductor element hardly manufactures a structure smaller than 100 nm. An electron beam or focused ion beam lithography can achieve a nanofabrication such as several nm to several ten nm, however, it requires a high processing cost and takes a long processing time. Accordingly, these techniques are hardly put to practical use.
On the other hand, the use of a self-organization such as particles, block copolymers, anodic porous alumina, synthetic DNA, etc. is an efficient method for producing the patterned media (see for instance, non-Patent Documents 2 to 4 and Patent document 1; non-Patent Document 2; S. Sun, C. B. Murray, D. Weller, L. Folks, A. Moser, Science 2000, 287, 1989., non-Patent Document 3; K. Naito, H. Hieda, M. Sakurai, Y. Kamata, K. Asakawa, IEEE Trans. Mag. 2002, 38, 1949., non-Patent Document 4; M. Shiraki, Y. Wakui, T. Tokushima, N. Tsuya, IEEE Trans. Mag. 1985, 21, 1465., Patent Document 1; Japanese patent Application Laid-Open No. 2000-190300). However, in forming a pattern by the self-organization, the pattern is formed in random array directions at random positions on a board. Accordingly, the regularity of a structure is hardly strictly controlled to generate turbulence or defects in the arrangement of the nanoscale magnetic material. In the patterned media, the turbulence or the defects in the arrangement of the magnetic material undesirably cause an error during recording and reproducing data.
A nanoimprint method is a method for simultaneously transferring a pattern of a mold to a resist on a board by using the mold processed by an electron beam lithography and can achieve an efficient and regular nanofabrication can be realized (see for instance, non-Patent Document 5; S. Y. Chou, P. R. Krauss, P. J. Renstrom, Appl. Phys. Lett. 1995, 67, 3114.). Also by this method, the patterned media can be efficiently formed. However, the patterned media in which the regularity of the mold pattern is precisely reproduced is hardly manufactured owing to a pattern transfer process by a mold press to the resist and a resist pattern transfer process to a magnetic layer by etching.
Methods for producing various kinds of patterned media are described in detail in non-Patent Document 6; C. A. Ross, Annu. Rev. Mater. Res. 2001, 31, 203.
As described above, the patterned media is proposed as a next generation high-density magnetic recording media. However, as the method for producing the patterned media, an efficient and accurate nanoscale processing technique has not been yet developed. Therefore, the patterned media in which groups of magnetic nanoparticles having a substantially uniform size are arranged in an array on a board and the efficient and regular nanofabrication method have been desired to be established.
Further, in recent years, various kinds of nanoscale particles have been developed as well as the magnetic nanoparticles. As such nanoparticles, for instance, semiconductor nanoparticles, conductive nanoparticles, ferroelectric nanoparticles, phase change nanoparticles, photochromic nanoparticles, thermochromic nanoparticles, electrochromic nanoparticles, etc. may be exemplified. For these nanoparticles, the technique for accurately arranging the groups of nanoparticles in an array on the board is applicable to a variety of uses.